Abstract
A typical Rho-independent terminator of transcription was found at the end of the histidine operon of Salmonella typhimurium. This site is used to terminate, in addition to the his operon mRNA, a 1,200-nucleotide RNA of unknown function transcribed on the opposite strand. The efficiency of termination of transcription at this site was investigated in vivo and in vitro by cloning of the terminator structure in either orientation in vector systems used to study regulatory signals. Termination of transcription at this site was very efficient, both in vivo and in vitro, and in both orientations.